A petroleum tanker trailer utilizes large diameter piping or “wet lines” for delivery of flammable product to service stations as well as for loading product into the trailer. After the trailer is loaded, up to 75 gallons of flammable liquid remain in the wet lines. Accordingly a collision proximate the wet lines can spill up to 75 gallons of flammable liquid and can cause severe injury or death along with major property damage.
Various approaches have been proposed to address this problem. One solution is to drain the fluid from the wet lines after filling. The problem with this approach is one of weights and measures. Since the tanker trailer is effectively considered as having received the fuel in the wet lines, pumping this fuel back into the supply tank produces accounting headaches and requires that the fuel that is siphoned off be measured and credit given accordingly. This is both a complex and costly undertaking.
Another approach is to provide a protective cage around the wet lines. This however is economically unattractive since it adds significant weight to the tanker trailer which translates into lower fuel cavity capacity.
Yet another approach is to force a gas into the wet lines to force the liquid remaining in the wet lines after the filling process back into the tank of the tanker trailer. This procedure requires tremendous pressure to force the fuel back into the housing tank against the downward gravity force of the fuel in the housing tank. As a result, powerful pumps or other mechanisms have to be made available, greatly adding to the cost of the filling and unloading operations.
Another approach is to provide a suction pump which is controlled by the truck supplied air and which is operative to pump liquid in the wet lines from the wet lines back into the holding tank on the trailer itself. This approach typically utilizes a sensor which senses the presence of liquid in the wet lines and actuates the pump to drain the wet lines. Although this approach is generally satisfactory it requires, for each truck, that the API (American Petroleum Institute) adaptor heads for each truck be replaced with a customized API head to accommodate the evacuation system.